The invention relates to spectacle frames of the split rim type, usually made of metal materials, with the rim member having a cross sectional indentation to hold the beveled edge of the lens securely. The split allows the opening of the rim when inserting or removing a lens, and endpieces are attached to the ends of the split, by solder or other means, in order to provide a method for locking the split in a closed position.
It is important that the ends of the split be held firmly together so that the lens will be locked securely in place. A lens falling out of a frame is a major inconvenience to the wearer, and frequently results in the expense of a broken lens having to be replaced. Whatever means is used for holding the split closed must not only keep the frame closed tightly, but at the same time allow the frame to be opened for occasions where the replacement of a lens may be necessary.
In the history of related art, screws have been by far the most commonly used method for holding these described endpieces together and keeping the split rim tightly closed around the lens. Unfortunately, it is very common for such screws to gradually work loose, causing a lens in some cases to fall out. Even in cases where the lens may not fall out, it is still possible that the lens can rotate within the frame, thus altering the optical properties of the glasses when prescription lenses are involved. It is particularly critical that the cylinder axis of a lens for the correction of astigmatism is maintained in the proper rotational alignment to be effective. Therefore, even minor loosening of the frame is undesirable.
The threads of the typically tiny screws used, as well as the receptor threads in the eyeglass frame, often cause additional problems by stripping out. Quite frequently a perfectly good frame can be rendered useless only because of stripped threads. A nut and bolt combination can often provide a makeshift solution to this problem, but is generally unattractive and is also subject to loosening.
Many previous attempts have been made to solve the drawbacks of screws for this application, but have been either ineffective or have introduced other disadvantages. The continued predominance of the use of screws in this regard is a strong indication of the failure of previously proposed methods to adequately fulfill all of the requirements of spectacle frames.
Designs using clips which slide or snap either onto the eyewire endpieces (patent #'s 308,344 & 2,006,917) or over the screw to prevent it from backing out ( #1,882,153) have been proposed. Another approach has been the bending of certain parts to prevent loosening of the frame (#735,917) or turning of screws (#2,740,327). The problems introduced by these designs are numerous. In some cases they make insertion of the lenses during assembly of the eyeglasses awkward, which is an important consideration for the many optical laboratories which provide one hour service, where ease and speed of assembly are required. In other previous attempts the option of replacing a lens which may have been accidentally broken is impractical, particularly when parts of the frame must be restraightened and bent again during the lens replacement, leading to problems with metal fatigue. Sometimes the extra parts attached to the frame may be bulky and compromise the visual appeal of the eyewear, which is an important consideration of eyeglass wearers. In other previously designed systems, springs have been used to maintain a closing force on the opening in the eyewire (#'s 3,473,839, 3,609,018, 4,256,387, 4,360,252 & 4,813,775). None of these approaches solve the problems of screws without introducing others. In many cases, the frames are designed so that they can only be partly opened for lens insertion or removal. This can lead to problems and even hazards when trying to insert or remove glass lenses which can chip under these circumstances, thus causing lens spoilage. Some of the designs are not suitable for frames made of thin metal materials, therefore having limited application to only certain other types of frames. In other cases, the design does not allow any tolerance for lenses having anything but an absolutely precise fit for the frame. If the lenses are even the slightest amount too large, the device will not allow closure of the frame. Other methods, such as toggle levers or cam type arrangements have also been proposed ((#'s 2,730,012, 2,73,709 & 2,754,724) but are generally too bulky in appearance to be suitable for delicate frames made of thin materials. Soldering the frame closed has even been proposed (#2,104,503), but this is clearly impractical because of the adverse effects the high temperatures would have on plastic lens materials, as well as difficulties with lens replacement. Still another approach has been the design of frames where the screws are mounted transversely to the plane of the lens (#'s 1,590,719 & 3,762,804). These designs still use conventional screws, however, and in addition sometimes make assembly of the glasses more difficult because the frame must be held in a tightly closed position while the screw is being inserted. Those skilled in the art will readily admit the difficulty of holding a frame closed and keeping the lens positioned properly while simultaneously trying to engage the threads of a tiny screw into the frame.